This invention relates to the synthesis and isomerization of 1,2-bis(indenyl)ethanes (EBI).
In this specification, the expression 1,2-bis(indenyl)ethane or EBI means collectively all isomers of Formula I: 
in which the symbol xe2x80x9c(xe2x80x9d indicates a 1,2-bis(indenyl-1)ethane which has a 1,2, 1,2xe2x80x2 double bond (thermodynamic EBI, BRN No. 3055002, CAS RN No. 18657-57-3) or a 2,3 2xe2x80x2,3xe2x80x2 double bond (kinetic EBI, BRN No. 3083835, CAS RN Nos. 15721-07-0, 18686-04-9, 18686-05-0). The two unnumbered fusion C atoms are asymmetric. The 1,1xe2x80x2C atoms are asymmetric in kinetic EBI compounds. The 3,3xe2x80x2 C atoms are asymmetric when substituted.
Each of the ring substituents may be hydrogen or any one to ten carbon atom hydrocarbyl group. Each ring substituent may be the same as or different from any other ring substituent. One to ten carbon atom alkyl groups are preferred. 2,2xe2x80x2 methyl and 4,7, 4xe2x80x27xe2x80x2 dimethyl EBIs are representative.
The EBI 3,3xe2x80x2 substituents may be any hydrocarbyl group or hydrocarbyl silyl group, preferably having one to ten carbon atoms. Useful alkyl silyl 3,3xe2x80x2 substituents have the formula (R)3xe2x80x94Si, in which R is a one to ten carbon atom hydrocarbyl group, typically an alkyl group. The methyl group is preferred. Each R may be the same as or different from each of the other two R groups. Chiral TMS-EBI is preferred.
Meso and rac (racemic) forms of kinetic EBI and thermal isomerization of kinetic to thermodynamic EBI are known phenomena. Marxc3xa9chal, et al, Bulletin de la Societe Chimique de France (1967) 8:2954-2961.
Kinetic and thermodynamic EBI are interchangeably useful separately and in mixtures as ligands for metallocene olefin polymerization catalysts. However, the large-scale production of kinetic EBI is constrained because the thermodynamic isomer is produced at temperatures below about xe2x88x9270xc2x0 C.; whereas, at higher temperatures low yields of kinetic EBI consequent from spiro indene and vinylidene impurities may result. See, e.g., Yang, et al., SYNLETT (1996) 147 and Collins, et al., J.Organometallic Chem. (1988) 342:21 (thermodynamic EBI synthesized at xe2x88x9278xc2x0 C. stirred overnight and warmed to room temperature). See also, Ewen, J., et al., J.Am.Chem.Soc. (1987) 109:6544-6545 and Grossman, R., et al., Organometallics (1991) 10:1501-1505 (50% to 80% recrystallized yields of thermodynamic isomer because of the formation of spiroindene by-product).
3,3xe2x80x2 C. substitution imparts chirality to some Formula I compounds with consequent achiral meso and chiral racemic forms. Metallocene isotactic polypropylene catalysts may require substantially pure rac EBI ligands; for example, rac 1,2-bis(3,3xe2x80x2trimethylsilyl indenyl-1)ethane (hereinafter rac TMS-EBI). Typically, TMS-EBI may be produced by reaction of EBI with two equivalents of BuLi to produce dilithio EBI. Dilithio EBI is treated with two equivalents of TMSC1 to produce 3,3xe2x80x2-bis TMS-EBI. Synthesis of substituted EBI compounds, including TMS-EBI, typically yields a mixture of meso and rac forms. Separation of the rac form from such mixtures may not be practical for industrial applications.
The invention may comprise a method for producing EBI from an indene in good yield at moderate temperatures.
Pursuant to one aspect of the invention, a method is provided for the moderate temperature synthesis of kinetic EBI substantially free of by-product impurities.
Important embodiments of the invention include isomerization agents effective to convert kinetic EBI to thermodynamic EBI and also to convert meso 3,3xe2x80x2 substituted EBI to a meso/rac mixture. The invention may include isomerization protocols implemented by these reagents.
The invention may include a series of moderate temperature steps to produce a reaction mixture from which solid kinetic EBI which may be substantially free of spiro indene impurities is separated from a mother liquor. The solid kinetic EBI may be separated in a single increment or in a plurality of increments, each of said increments being separated from the mother liquor of the preceding increment. Each mother liquor may comprise a solution of additional kinetic EBI which may be isomerized to thermodynamic EBI, preferably in solution in its mother liquor which is cooled induce precipitation of solid thermodynamic EBI. The solid kinetic and thermodynamic EBI products are useful separately or in combination as metallocene catalyst ligands. This procedure for synthesizing thermodynamic EBI, which includes an isomerization step, is practiced and scalable, and is an improvement over the lower yielding preparation of thermodynamic EBI which requires starting the reactions at temperatures below xe2x88x9270xc2x0 C. reported in the cited references.
The invention may include isomerization of a meso 3,3xe2x80x2 substituted EBI, such as TMS-EBI to yield a meso and rac mixture. Treatment of an existing mixture of meso and rac 3,3xe2x80x2 substituted EBI with the isomerization agent yields a product mixture enriched in the rac isomer. The stereospecific transformation of racemic TMS-EBI to racemic metallocene is known. See, e g., Nifant""ev, I. A., et al. (1997) Organometallics 16:713-715. However, racemic TMS-EBI was isolated in only 34% crystallized yield from the reaction of dilithio EBI and a trimethyl silicon chloride. The isomerization of meso to meso-rac TMS pursuant to this invention is an improvement over the prior art because racemic TMS-EBI is used to synthesize racemic metallocene. Iteration of the isomerization reaction with rac enrichment of the product mixture at each iteration may yield an ultimate substantially pure, e.g., 96% pure, rac product useful as a stereospecific metallocene olefin polymerization catalyst ligand.
Formula I EBIs produced by any of the several known methods may be used in any one or more of the embodiments of the invention.
The isomerization agents useful in this invention are solutions of alkali metal alkoxides having the formula MOR, wherein M is any alkali metal and R is as defined. In the preferred isomerization agents, R is t-butyl.
Useful isomerization agents are alkali metal alkoxide solutions in a non-interfering, preferably ether, solvent. Suitable solvents include tetrahydrofuran, 2-methyl tetrahydrofuran, dioxane, and 1,2-dimethoxyethane. The isomerization agent solution may contain any functional concentration, e.g., from 10 mol percent to 20 mol percent, of alkali metal alkoxide. The preferred isomerization agent is a 10 to 20 mol percent solution of potassium tertiary butoxide in tetrahydrofuran.
The isomerization reagents convert kinetic EBI to thermodynamic EBI. They also convert meso 3,3xe2x80x2-substituted chiral EBI to a mixture of the meso and rac forms.
In general, the isomerization reaction is accomplished by treatment of a kinetic EBI or meso 3,3xe2x80x2-substituted EBI with the isomerization reagent under conditions and for a time effective to accomplish the desired reaction. Selection of the appropriate conditions for a particular isomerization is determined by the skilled man as a function of the particular isomerization involved and of the degree of conversion desired. It is known that by going from sodium methoxide to potassium t-butoxide, a substantial increase in basic strength as well as more favorable solubility in ether is achieved. See, Gilman (1953) Organic Chemistry Vol. III, pp. 4-5, citing Gould, Jr., et al. (1935) J.Am.Chem.Soc. 57:340, and Renfrow (1944) J.Am.Chem.Soc. 66:144.
Each type of isomerization may be accomplished to some degree by treatment of the particular EBI isomer with an isomerization reagent at a temperature of from about 20xc2x0 C. to reflux for a time period of 30 minutes to 12 hours. The kinetic to thermodynamic EBI isomerization appears to be facilitated by a higher temperature and a longer time than the 3,3xe2x80x2-bis TMS-EBI meso to meso:rac mixture isomerization. For example, 100% conversion of kinetic to thermodynamic EBI may be accomplished by overnight reflux in the reagent solvent such as THF. Less than 100% isomerization occurs at lower temperatures or in a shorter reflux time. In contrast, 100% meso TMS-EBI is converted in 30 minutes at room temperature (20xc2x0 C.) by a similar isomerization agent to a 50/50 rac-meso mixture.
This aspect of the invention relates to the recovery of kinetic EBI from a synthesis reaction mixture. An important step entails exchange of any non-hydrocarbon reaction mixture solvent for a hydrocarbon solvent from which kinetic EBI may be precipitated, e.g., by cooling with consequent crystallization. Appropriate hydrocarbon solvents are five to eight carbon atom alkanes. Hexane and commercially available mixtures of hexanes preferred. Aromatic hydrocarbon solvents including benzene, toluene, and xylene may be used having due regard to conditions requisite to crystallization from a particular solvent.
The hydrocarbon solution of kinetic EBI is cooled to cause precipitation of at least a portion of solute. The quantity of kinetic EBI precipitated is a function of the conditions imposed. The solid kinetic EBI is separated, typically by filtration, from the mother liquor solution of additional kinetic EBI. The separated solid kinetic EBI is dried. A yield of 20% to 50% from indene is typical.
This mother liquor or filtrate from the separation of solid kinetic EBI is treated with an isomerization agent as described in Sections 4 and 5, wherein the kinetic EBI solute is converted to the thermodynamic isomer. The isomerization reaction mixture is cooled or otherwise treated to induce precipitation of thermodynamic EBI. The precipitate is recovered. The combined yield of solid kinetic and thermodynamic EBI from indene may exceed 60%.
Either the separated kinetic EBI product of step 5, or the separated thermodynamic product of step 6, or a mixture thereof may be used in subsequent procedures to yield other products. An important aspect of this invention is the substantial combined yield of both EBI isomers from indene at relatively low reaction temperatures. The EBI product mixture is used in known manner to produce, inter alia, metallocene olefin polymerization catalysts having the formula
A2ZX2
in which A is a mixture of kinetic and thermodynamic EBI, Z is Zr, Ti or Hf, and X is a halogen. Z is typically Zr and X is typically chlorine. (EBI)2ZrCl2 is a typical catalyst. Typically, such metallocenes are produced by the reaction of a ligand lithenide with a Group IV tetrahalide. See, generally, Spaleck (1994) Organometallics 13:954-963, Journal of Orpanometallic Chem. 288 (1985) 63-67, and various Spaleck patents, including U.S. Pat. Nos. 5,145,819 and 5,278,264.